interface speak {
    sing(music:string):void
}

interface run {
    go():void
}

// js中定义的也是单继承？
interface total extends speak {
    go():void
}
class phone implements speak{
    sing(music: string) {

    }
    
}

class car implements speak,run{
    sing(music: string) {

    }
    go(){

    }
}

class car2 implements total{
    sing(music: string) {

    }
    go(){

    }
}